Japanese patent application no. 2000-292028, filed Sep. 26, 2000, is hereby incorporated by reference in its entirety.
The present invention relates to an oscillation circuit and an electronic circuit, and a semiconductor device, a timepiece and electronic equipment provided with the same.
The oscillation circuit used in a portable wristwatch or electronic equipment often has a configuration such that a principal circuit portion thereof that is formed on a semiconductor substrate is connected by input-output terminals to a crystal oscillator provided at a separate location on that semiconductor substrate. For that reason, an electrostatic protection circuit is provided on the input-output terminal side of that principal circuit portion, to protect that principal circuit portion from any surge voltage intruding from the exterior through those input-output terminals.
However, in such a conventional circuit, the power source of the oscillation circuit drive is utilized for bypassing surge voltages of the electrostatic protection circuit, so that if there should be a change in the power-supply voltage of the oscillation circuit for some reason, that would cause a change in the parasitic capacitance of that electrostatic protection circuit and, as a result, that would raise a problem in that the oscillation frequency of the oscillation circuit will change.
An objective of the present invention is to provide an oscillation circuit and an electronic circuit which enable protection of the principal circuit portions thereof from any surge voltage that intrudes from the exterior through input-output terminals, and which can oscillate at a stable frequency without being affected by changes in the power-supply voltage of the oscillation circuit, together with a semiconductor device, a timepiece and electronic equipment that are provided with the oscillation circuit and the electronic circuit.
(1) To achieve this objective, an oscillation circuit in accordance with the present invention comprises:
a first electrostatic protection circuit connected between a signal path of the oscillation circuit and a constant-voltage side, and bypassing an electrostatic voltage of a first polarity that intrudes into the signal path to a side of a constant bypass voltage through a first semiconductor rectifier element; and
a second electrostatic protection circuit connected between the signal path and a reference potential side, and bypassing an electrostatic voltage of a second polarity that intrudes into the signal path to the reference potential side through a second semiconductor rectifier element,
wherein the constant bypass voltage is set to a value such that the first and second semiconductor rectifier elements are not turned on by voltage change in the signal path caused by a leakage current, even when a leakage current is generated between the signal path and a power-supply voltage line.
In this case, when it is assumed that the power-supply voltage is VSS, the forward-direction on-voltage of the semiconductor rectifier element is VFon, and the potential difference between the signal path and the power-supply voltage line when a leakage current is generated is VR; the constant bypass voltage Vreg may be set in such a manner that the following inequality is satisfied, within a range of expected operating voltages of the power-supply voltage |VSS|:
|Vreg| greater than |VSS|xe2x88x92VRxe2x88x92VFon
The constant bypass voltage may be a constant voltage Vreg1 that is supplied separately from a constant voltage Vreg2 supplied as a power-supply voltage for the oscillation circuit.
The constant bypass voltage Vreg1 the constant voltage Vreg2 supplied as the power-supply voltage of the oscillation circuit maybe set in such a manner that the following inequality is satisfied:
|Vreg1| greater than |Vreg2|
One voltage Vreg2, which is one of a supplied constant voltage from a constant voltage supply circuit and a constant voltage obtained by dividing or stepping up the supplied constant voltage, may be used as a power-supply voltage for the oscillation circuit, and the other voltage Vreg1 may be used as the constant bypass voltage.
A constant voltage having a temperature characteristic that ensures a small voltage variation with respect to a temperature change may be used as the constant bypass voltage. For example, a constant voltage for driving a temperature sensor can be used as this constant bypass voltage, since it has a temperature characteristic with a shallow slope.
A discharging semiconductor rectifier element for discharging an electrostatic voltage of a first polarity that intrudes into the signal path to a side of a constant bypass voltage through the first semiconductor rectifier element, may be provided between an output of the constant voltage supply circuit which supplies the constant bypass voltage and the reference potential.
(2) An electronic circuit may be formed by using an oscillation circuit in accordance with the present invention.
This electronic circuit may comprise the oscillation circuit and a drive circuit which drives a driven section, based on an output of the oscillation circuit.
This makes it possible to obtain an electronic circuit that enables satisfactory operation using a stable frequency output supplied from the oscillation circuit.
A semiconductor device may be formed by using an oscillation circuit or electronic circuit in accordance with the present invention.
In other words, if an oscillation circuit that uses a crystal oscillator or an electronic circuit using such an oscillation circuit is formed on a semiconductor device, the principle circuit portions of the oscillation circuit formed on the circuit board are often connected by wiring to a crystal oscillator provided in a different area of that circuit board. In such a case, there is a danger that electrostatic voltages such as surge voltages will intrude as noise from the connections between the crystal oscillator and the principal circuit portions, damaging the interior of the circuitry.
In that case, too, the present invention makes it possible to use an electrostatic protection circuit to remove an electrostatic voltage such as a surge voltage that may intrude into the circuitry, and thus implement a semiconductor device that can drive the various parts of the circuit in a favorable manner using a stabilized oscillation output.
A timepiece may be formed by using an oscillation circuit or electronic circuit in accordance with the present invention. This timepiece may comprise an oscillation circuit and a time display section which displays a time based on the oscillation circuit.
The present invention makes it possible to provide a timepiece that can keep accurate time without being affected by variations in the power-supply voltage of the main power source thereof.
Electronic equipment may be formed by using an oscillation circuit or electronic circuit in accordance with the present invention.
Electronic equipment may be configured to comprise an oscillation circuit, a drive circuit which drives a driven section, based on an output of the oscillation circuit, and the driven section.
This makes it possible to implement electronic equipment that can generate an accurate oscillation output that is not affected by any changes in the power-supply voltage of the oscillation circuit, to cause the operation of the parts of the circuitry.
In particular, a timepiece or electronic equipment that uses an oscillation circuit or electronic circuit in accordance with the present invention is extremely suitable as a portable timepiece or other item of electronic equipment that uses an exchangeable battery or a rechargeable battery as a main power source.